hmmm... this is something that you have to manually enable? I'm gonna have to look into this. When I still had the AISuite monitoring my gack it seemed everything was getting piled into the first core but I don't know much about this stuff.

Once I disabled startup programs AISuite stopped working and frankly it was a mistake installing it in the first place. Bugger won't uninstall though so I get a stupid warning every time a boot up.

The problem isn't with SONAR, which uses multithreading quite well, but with plugins. In a heavily-loaded project, 90% or more of the processing time may be spent within plugins. Having a highly-optimized engine doesn't do much good when relatively few of the total CPU cycles are spent there. 

SONAR has to treat each track as a single thread due to the fundamentally sequential nature of the signal chain. It can spawn threads for things like video updates, but the audio signal flow within a given track is necessarily a do-this-then-do-that serial process. Consequently, any one plugin in the track's fx bin can dictate the efficiency with which audio is processed in that track.

Some plugins support multi-threading, but most do not. Of the ones that do, most actually work better single-threaded because what's happening within the plugin is also serial in nature. 

So yes, SONAR is multi-threaded and makes good use of multiple cores and multiple CPUs, but ultimately it's the third-party components that determine overall system load and efficiency.

+1 to above which is why the first core always hits red way before any of the others.... Which to me almost makes it all pointless as I don't think many people run a DAW without plugins. I'm sure there is a way for me at least to improve the ratios here as X1 on win7 x64 gave me many more soft synths/plugins at a recordable latency than X2 does on win8 with a fresh install.
However, saying that, with the right buffer settings, it works incredibly well  when mixing.
I'm hoping someone can teach me something here.

Bibs

I think the ThreadSchedulingModel variable in aud.ini still defaults to 1, so you could try setting that to 2 and see if it helps, although I don't know if Noel has made any changes to the code that makes that variable obsolete at this point.